Guide vanes of turbo machinery, particularly where a gas turbine plant is concerned, are exposed directly to the hot gases flowing out of the combustion chamber and are consequently subjected to high thermal loads which, in modern gas turbine plants, lie well above the material-specific thermal load-bearing limits of the individual components. For this reason, the gas turbine components, such as, in particular, the guide vanes and rotor blades, which are exposed directly to the hot gases, have to be cooled so that it can be ensured that the respective components do not overheat and suffer any irreversible damage caused by thermally induced material deteriorations. Cooling measures of this type are known in many different forms and normally involve a directed supply of cooling air to the individual components to be cooled, the cooling air being part of the compressed combustion air which emerges from the compressor unit of the gas turbine plant and which is branched off and is therefore unavailable for the further combustion operation.
It is obvious that the cooling air quantity branched off from the compressed supply air for cooling purposes must be kept as low as possible, so as not permanently to influence the performance of the gas turbine plant. Moreover, it is appropriate for the branched-off cooling air fraction to be routed as effectively as possible and without losses, in particular without leakage losses, to the individual gas turbine components to be cooled. With regards the guide vane concept described below, it is appropriate to utilize effectively and without leakage losses the cooling air which is supplied to a guide vane for cooling purposes.
FIGS. 2a and 2b illustrate respectively a side illustration and a cross-sectional illustration of the radially outer part region of a guide vane 1 with an adjacent stator-side supporting structure 2. FIG. 2a shows an axial side view of a guide vane 1 which issues radially inward into the flow duct K. A rotor blade La is indicated highly diagrammatically, offset axially with respect to the guide vane 1. The guide vane 1 has in a way known per se an inner duct system KS which may be gathered from the cross-sectional picture illustrated in FIG. 2b and drawn along the sectional plane A-A. To cool the guide vane 1, compressed cooling air L is supplied to the guide vane 1 through a cooling air supply duct SC provided on the stator side.
The guide vane 1 is composed of a guide vane leaf 3 (see FIG. 2b), of a platform 4 adjoining the guide vane leaf 3 radially on the outside and of a connecting structure 5 which lies opposite the guide vane leaf 3 in relation to the platform 4 and by means of which the guide vane 1 is fastened in the supporting structure 2 of the casing of the turbomachine or of the gas turbine plant. The platform 4 has in this case a first surface 41 facing the flow duct K and a second surface 42 facing away from the flow duct K. The connecting structure 5 projects radially beyond the plane of the platform surface 42 and with its side wall portions 51 and 52 and the end-face side wall portions, not illustrated in FIG. 2b, surrounds an inner cavity 6 which is connected, open, on the one hand, to the cooling air supply duct SC and, on the other hand, to the cooling duct system KS of the guide vane 1. The lateral dimensioning of the cavity 6 in the plane of the platform surface 42 is preferably selected such that the cross-section obtained in a radial projection onto the guide vane leaf 3 of the guide vane 1 is covered preferably completely by the cavity 6, so that all the cooling ducts KS incorporated within the guide vane leaf 3 can be supplied with cooling air L from the cavity 6. This ensures an optimal supply of cooling air to the guide vane leaf 3.
The fastening of the guide vane 1 within the supporting structure 2, mostly of annular design, takes place in recesses 2′ which run longitudinally within the supporting structure 2 and into which issue laterally joining contours 7 of collar-shaped design which project beyond the side wall portions 51 and 52 at their upper region. The joining tolerances between the recesses 2′ and the joining contours 7 of collar-like design are selected such that, on the one hand, rapid assembly by the joining contours being smoothly introduced longitudinally into the recesses of groove-shaped design is possible, but, on the other hand, gastight pressure between the joining contours and the recesses is ensured for operationally induced heating and associated material expansion, so that no cooling air entering the cavity 6 through the cooling air supply duct SC can pass through the joining connection described above.
For operational and also assembly reasons, an intermediate gap 8 is provided between the radially outermost boundary face 9′ of the side wall portions 51 and 52 and the inner contouring of the supporting structure 2 and extends, perpendicularly to the drawing plane illustrated in FIG. 2b, over the entire longitudinal extent of the fastening structure 5 and consequently over the end-face wall portions 53 and 54 (FIG. 2a). The intermediate gap 8, which is also formed between the end-face wall portions 53 and 54 and the radially opposite supporting structure 2, affords the cooling air flowing into the cavity 6 an excellent possibility of escaping through adjacent gaps. Leakage paths in respect of this may be gathered from FIG. 2a with reference to the arrowed illustrations representing in this the leakage flows. Thus, the cavity 6 is supplied from the cooling air supply duct SC with the main cooling air flow, from which part flows can escape laterally, on both sides, through the respective intermediate gaps 8 via the top edges of the end-face wall portions 53 and 54. The laterally escaping cooling air part streams, on the one hand, pass between radially running intermediate gaps 9 between the supporting structure 2 and axially adjacent guide vane casing regions and can ultimately pass, unused, via further intermediate gaps into the flow duct K (see the dashed arrowed illustration). It is appropriate to avoid leakage losses of this type, but without impairing the operating behavior and mountability of the individual components.